Renal artery stenosis is an important cause of hypertension and renal failure. The most common disease process that results in renal artery stenosis is atherosclerosis. Detection of renal artery lesions by noninvasive means has been a difficult problem, and until recently invasive arteriography was the only reliable method. However, during the past few years, ultrasonic duplex scanning has emerged as an accurate technique for screening patients who are considered to be at risk for renal artery disease. In addition, this same noninvasive approach can be used for serial follow-up of these patients to document the changes that occur in the renal arteries over time. An important issue which has never been rigorously addressed is the natural history of renal artery lesions. It is currently unknown whether renal artery stenoses are likely to progress, what the rate of progression might be, and whether renal artery occlusion is a significant possibility. The status of renal function and renal mass associated with renal artery stenosis are also important considerations. It is estimated that up to 100,000 patients per year will develop ischemic renal failure secondary to progressive bilateral renal artery atherosclerosis. The investigators point out that if the risk and rate of disease progression in the renal arteries could be defined, it would be a major accomplishment that could have significant implications for patient management. The proposed project will initiate long-term follow-up studies in patients with documented renal artery stenosis. This will be accomplished by the use of duplex scanning at 6 to 12 month intervals. The status of the renal arteries, renal size, renal function, and clinical data regarding blood pressure control and risk factors for atherosclerosis will be monitored. These data will be analyzed to determine the rate of renal artery disease progression and the value of specific clinical variables as predictors of disease progression. The observed changes in renal artery disease severity will also be correlated with the severity of arterial occlusive disease in the carotid and lower extremity circulations.